Minced or comminuted meat, e.g. for use in hamburgers, is traditionally produced from raw materials in the form of meat and fat obtained when processing or trimming carcass cuts and the like. The raw materials are coarsely comminuted down to a particle size of 10-15 mm and are placed in respective tanks or tubs, of which one e.g. contains pure meat and another one fat-containing meat or possibly pure fat. The desired composition of the finished product is provided by mixing the various types of meat and fat raw material in predetermined ratios, so that the mixture will fulfil certain specifications with regard to fat, protein etc. When the correct ratio has been achieved, the raw materials are mixed in the best possible manner without spoiling them by "overmixing". Then, the mixture is discharged from the tank and finally comminuted to the desired particle size, after which the product is used for making hamburgers, sausage meat or other products.
Especially the fat content in the raw materials can vary considerably, and for this reason it is necessary to determine the fat content once or a number of times to ensure that the finished product fulfils the specifications. Either a direct or an indirect method may be used to ensure that the finished product has the specified fat content.
The direct method consists in that the operator, on the basis of her or his experience, will introduce the various types of raw materials in the mixer in proportions estimated to make the mixture contain a surplus of meat. When the ingredients have been mixed, the operator takes a sample that is analysed for fat content. Based on the result of the analysis, the operator adjusts the mixture by adding a calculated amount of fat-containing raw material. After renewed mixing, a new sample is taken and analysed. The result of this analysis will normally fulfil the specifications, so that all that now remains is to complete the mixing process.
The method requires much time and effort to ensure that the finished product complies with the specifications. Even then, the content of the various ingredients in the finished product will vary considerably within the limits of the specifications, so that in may cases, the product will lie relatively far from the optimum. If adjustments and mixing operations have to be repeated too often, problems with so-called "overmixing" can arise, manifesting themselves as formation of fat smears and exudates, impairing the quality of the product. In many establishments, however, the method is preferred, as it is flexible and makes it possible to use the raw materials in their original state and without having to analyse them.
The indirect method consists in that each and every batch of raw materials is analysed for its content of fat, protein and water. In other words: from each and every container or tub containing raw material, samples have to be taken and analysed. After this, the results of the analyses are used to calculate the quantity of each type of raw material to be used for producing a finished product with predetermined specifications. The calculation is preferably carried out using a special computer program, as it may be necessary to use 5-10 different types of raw materials. If all instructions are followed, the finished product will comply with the specifications.
This method tends to be preferred by an increasing number of establishments, as it makes it possible to avoid "overmixing" and to come closer to the optimum composition or to comply with stricter specifications.
With both methods, the fat content is determined by means of one of the usual methods of analysis in the meat-processing industry, of which some are carried out "at line", i.e. by the operator in the processing room, and some "off line", i.e. by an assistant in a separate laboratory. The first type of methods of analysis comprises the determination of fat by means of X-ray (Anyl-Ray) and determination of specific weight (Scanalyser). The latter type comprises wet chemical analysis, Fosslet analysis, NIT-transmission measurement (Tecator) and NIR-reflection analysis.
Both of these methods require the operator to be skilled in taking a sample that is representative of the full amount of material.
U.S. Pat. No. 4,844,619 (Weiler & Co.) discloses a specially designed mixing machine provided with a device for taking samples to be analysed for their fat content. The machine comprises an elongate mixing tub and a worm conveyor placed in a longitudinal recess in the bottom of the tub. The worm serves to move material from one end of the tub to the other end during the mixing process. When the worm rotates in one direction, it can also convey new raw material into the tub, while with the opposite direction of rotation, it can convey a fully mixed meat product out of the tub.
The device for taking samples is placed below the mixing tub and is constructed like a meat mincer with a worm. Meat material from the recess in the mixing tub falls down into the meat mincer, and the latter advances it against a perforated disc with a rotating knife, finally mincing the material to a suitable particle size. When the material in the mixing tub is to be analysed, the meat mincer is started and a suitable quantity of finely minced sample is collected at the end of the mincer. The fat content of the sample is determined in a separate measuring equipment operating by means of X-rays.
With this mixing machine it is not required that the operator is skilled in taking a representative sample. The sample, being automatically taken out and finely minced by means of the meat mincer, should be representative of the material in the mixing tub, because the worm conveyor in the recess in the tub causes the different raw materials to be mixed with each other.
U.S. Pat. No. 4,171,164 (The Kartridg Pak Co.) discloses a system, in which meat without fat and meat containing fat, respectively, are introduced into a mixing tub in proportions giving a certain percentage of fat in the product in the tub after mixing. The system may comprise two separate lines, each advancing a respective type of raw material to the mixing tub.
Firstly, the raw materials are coarsely comminuted to a particle size of 10-15 mm, and are then pumped to respective measuring devices, using dual-energy X-ray for continuously determining the fat content in each type of raw material. After this, the material flow of each type of raw material is measured by means of hopper devices collecting material and acting upon some weighing cells. Finally, the two types of raw material are introduced together in the mixing tub. The percentage of fat in the mixing tub may be computed continuously based on the measuring results. The ratio between the flow of the two material streams is controlled so as to finally achieve a mixture with a predetermined percentage of fat. E.g., the pump in one of the lines can run with a constant output and the pump in the other line with a varying output depending on the instantaneous and integrated measuring results.
The raw materials having been introduced together in the tub are mixed to form a homogeneous mass that is discharged into a hopper and finely minced to the desired product, e.g. sausage meat.
This system requires a considerable quantity of equipment to be provided and maintained. Further, it is based upon the material passing unchanged through the analysis and on measuring all the material. These conditions can only be met by extremely few methods of analysis.